diff --git a/A2Mac/ViewController.swift b/A2Mac/ViewController.swift
index d8bd418..65851bf 100644
--- a/A2Mac/ViewController.swift
+++ b/A2Mac/ViewController.swift
@@ -429,6 +429,7 @@ class ViewController: NSViewController {
         mhz = freq
         MHz_6502 = UInt64(mhz * M)
         clk_6502_per_frm = MHz_6502 / UInt64(fps)
+        clk_6502_per_frm_set = clk_6502_per_frm
     }
 
     @IBAction func speedSelected(_ sender: NSButton) {
diff --git a/A2Mac/src/cpu/6502.c b/A2Mac/src/cpu/6502.c
index f4c6e3f..de465c6 100644
--- a/A2Mac/src/cpu/6502.c
+++ b/A2Mac/src/cpu/6502.c
@@ -33,10 +33,12 @@ void ViewController_spk_dn_play(void);
 const unsigned long long int iterations = G;
 unsigned long long int inst_cnt = 0;
 
-const unsigned int fps = 30;
+//const unsigned int fps = 30;
 const unsigned long long default_MHz_6502 = 1.023 * M; // 2 * M; // 4 * M; // 8 * M; // 16 * M; // 128 * M; // 256 * M; // 512 * M;
 unsigned long long MHz_6502 = default_MHz_6502;
 unsigned long long clk_6502_per_frm = default_MHz_6502 / fps;
+unsigned long long clk_6502_per_frm_set = default_MHz_6502 / fps;
+
 
 unsigned long long tick_per_sec = G;
 unsigned long long tick_6502_per_sec = 0;
@@ -77,13 +79,56 @@ disassembly_t disassembly;
 #include "disassembler.h"
 #include "mmio.h"
 
-
 uint16_t videoShadow [0x1000];
 uint32_t videoMem [0x2000];
 uint32_t * videoMemPtr = videoMem;
 
 uint16_t HiResLineAddrTbl [0x2000];
 
+
+INLINE void set_flags_N( const uint8_t test ) {
+    m6502.N = BITTEST(test, 7);
+}
+
+INLINE void set_flags_V( const uint8_t test ) {
+    m6502.V = BITTEST(test, 6);
+}
+
+INLINE void set_flags_Z( const uint8_t test ) {
+    m6502.Z = test == 0;
+}
+
+INLINE void set_flags_C( const int16_t test ) {
+    m6502.C = test >= 0;
+}
+
+INLINE void set_flags_NZ( const uint8_t test ) {
+    set_flags_N(test);
+    set_flags_Z(test);
+}
+
+INLINE void set_flags_NV( const uint8_t test ) {
+    set_flags_N(test);
+    set_flags_V(test);
+}
+
+INLINE void set_flags_NVZ( const uint8_t test ) {
+    set_flags_NZ(test);
+    set_flags_V(test);
+}
+
+INLINE void set_flags_NZC( const int16_t test ) {
+    set_flags_NZ(test);
+    set_flags_C(test);
+}
+
+//INLINE void set_flags_NZCV( int test ) {
+//    set_flags_NZC(test);
+//    set_flags_V(test);
+//}
+
+
+
 void initHiResLineAddresses() {
     uint16_t i = 0;
     for ( uint16_t x = 0; x <= 0x50; x+= 0x28 ) {
diff --git a/A2Mac/src/cpu/6502.h b/A2Mac/src/cpu/6502.h
index ef1d5c7..6537859 100644
--- a/A2Mac/src/cpu/6502.h
+++ b/A2Mac/src/cpu/6502.h
@@ -15,6 +15,7 @@
 
 extern unsigned long long MHz_6502;
 extern unsigned long long clk_6502_per_frm;
+extern unsigned long long clk_6502_per_frm_set;
 
 
 typedef enum {
@@ -99,7 +100,8 @@ extern void hires_Update(void);
 
 extern double mips;
 extern double mhz;
-extern const unsigned int fps;
+
+#define fps 30
 
 extern void tst6502(void);
 extern void m6502_ColdReset(void);
@@ -107,46 +109,5 @@ extern void m6502_Run(void);
 extern void kbdInput ( uint8_t code );
 
 
-INLINE void set_flags_N( const uint8_t test ) {
-    m6502.N = BITTEST(test, 7);
-}
-
-INLINE void set_flags_V( const uint8_t test ) {
-    m6502.V = BITTEST(test, 6);
-}
-
-INLINE void set_flags_Z( const uint8_t test ) {
-    m6502.Z = test == 0;
-}
-
-INLINE void set_flags_C( const int16_t test ) {
-    m6502.C = test >= 0;
-}
-
-INLINE void set_flags_NZ( const uint8_t test ) {
-    set_flags_N(test);
-    set_flags_Z(test);
-}
-
-INLINE void set_flags_NV( const uint8_t test ) {
-    set_flags_N(test);
-    set_flags_V(test);
-}
-
-INLINE void set_flags_NVZ( const uint8_t test ) {
-    set_flags_NZ(test);
-    set_flags_V(test);
-}
-
-INLINE void set_flags_NZC( const int16_t test ) {
-    set_flags_NZ(test);
-    set_flags_C(test);
-}
-
-//INLINE void set_flags_NZCV( int test ) {
-//    set_flags_NZC(test);
-//    set_flags_V(test);
-//}
-
 
 #endif /* __6502_H__ */
diff --git a/A2Mac/src/cpu/instructions/6502_instr_call_ret_jump.h b/A2Mac/src/cpu/instructions/6502_instr_call_ret_jump.h
index 94dd16c..b903d54 100644
--- a/A2Mac/src/cpu/instructions/6502_instr_call_ret_jump.h
+++ b/A2Mac/src/cpu/instructions/6502_instr_call_ret_jump.h
@@ -65,6 +65,12 @@ INLINE void RTS() {
     dbgPrintf("RTS ");
     disPrintf(disassembly.inst, "RTS");
     m6502.PC = POP_addr() +1;
+
+    // disk accelerator would only work for a certain amount of time
+    // currently it is 200ms simulated times
+    if ( m6502.clktime - disk.clk_since_last_read > clk_diskAcceleratorTimeout ) {
+        clk_6502_per_frm = clk_6502_per_frm_set;
+    }
 }
 
 /**
diff --git a/A2Mac/src/dev/disk/disk.c b/A2Mac/src/dev/disk/disk.c
index fb05ab3..9e722bd 100644
--- a/A2Mac/src/dev/disk/disk.c
+++ b/A2Mac/src/dev/disk/disk.c
@@ -13,9 +13,12 @@
 
 
 disk_t disk = {
-    { 0, 0, 0 }, // phase
+    { 0, 0, 0 },    // phase
+    0,              // clk_since_last_read
 };
 
+const unsigned long long clk_6502_per_frm_diskAccelerator = 100 * M / fps; // disk acceleration bumps up CPU clock to 100 MHz
+const unsigned long long clk_diskAcceleratorTimeout = 200000ULL;
 
 
 // motor position from the magnet state
@@ -57,6 +60,9 @@ void disk_phase() {
         
 //        printf(", p:%d d:%d l:%d: ph:%u trk:%u)", position, direction, lastPosition, phase.count, woz_tmap.phase[phase.count]);
                 
+        disk.clk_since_last_read = m6502.clktime;
+        clk_6502_per_frm = clk_6502_per_frm_diskAccelerator;
+
     }
     else {
         // invalid magnet config
@@ -68,6 +74,8 @@ void disk_phase() {
 
 uint8_t disk_read() {
     dbgPrintf("io_DISK_READ (S%u)\n", 6);
+    disk.clk_since_last_read = m6502.clktime;
+    clk_6502_per_frm = clk_6502_per_frm_diskAccelerator;
     return woz_read();
 }
 
diff --git a/A2Mac/src/dev/disk/disk.h b/A2Mac/src/dev/disk/disk.h
index a443cd5..ff683f7 100644
--- a/A2Mac/src/dev/disk/disk.h
+++ b/A2Mac/src/dev/disk/disk.h
@@ -26,6 +26,7 @@ typedef struct phase_s {
 
 typedef struct disk_s {
     phase_t phase;
+    uint64_t clk_since_last_read;
 } disk_t;
 
 extern disk_t disk;
@@ -47,9 +48,11 @@ extern disk_t disk;
 
 extern const int magnet_to_Poistion[16];
 extern const int position_to_direction[8][8];
+extern const unsigned long long clk_6502_per_frm_diskAccelerator;
+extern const unsigned long long clk_diskAcceleratorTimeout;
 
-extern void disk_phase();
-extern uint8_t disk_read();
+extern void disk_phase(void);
+extern uint8_t disk_read(void);
 
 
 #endif /* disk_h */